1. Field of the Invention
This invention relates to an improved helical scan magnetic recording device. More particularly, it relates to a helical scan magnetic recording device having a folded mounting plate in order to permit a tape wrap on the circumference of a tape support mandrel which is intermediate the conventional 180.degree. and 360.degree. tape wraps.
2. History of the Art
The desirability of recording and replaying high speed information signals from television and from high speed digital computers has resulted in increasingly sophisticated magnetic recording devices. Conventional longitudinal scan magnetic recording devices are adequate to record and replay relatively low frequency signals in the audio range. But such devices are not adequate for recording information signals in the video frequency range because it is not practical to drive them to high linear tape speeds required for use at such frequencies.
As disclosed in U.S. Pat. No. 2,773,120 issued to E. E. Masterson, helical scan magnetic recording devices overcome the necessity for high linear tape speeds. A typical helical scan device comprises a relatively wide magnetic tape, a pair of cylindrical support mandrels, a rotor, and a magnetic head (recording or replaying) disposed upon the rotor. The mandrels are axially aligned and positioned end-to-end with a slight gap between them, and the rotor is aligned on the common mandrel axis to rotate in the gap between the two mandrels. In operation, the wide magnetic tape is wrapped helically about the support mandrels with its edges abutted across the gap between the cylinders, and the rotor carries the magnetic head around the gap to scan a diagonal track on the tape. In such a device, the rotor speed can greatly exceed the tape speed, thereby permitting greatly increased scanning rates.
Conventional helical scan magnetic recording devices, however, are based upon a limited conception of mounting arrangements which result in relatively cumbersome and inefficient devices. Typical conventional devices utilize a tape wrap of substantially 360.degree. such as is described in the above-identified Masterson patent or substantially 180.degree. such as is described in U.S. Pat. No. 3,691,315 issued to W. A. Ellmore.
The difficulties with the 360.degree. wrap devices are manifold. First, because the tape is wrapped about 360.degree. of the mandrel circumference, the magnetic heads carried on the rotor mechanically interact with the tape throughout the 360.degree. rotation of the rotor about the mandrel axis. Such a device precludes practical arangements for gradually increasing and decreasing the head penetration into the region normally occupied by the tape. Second, the 360.degree. wrap device is relatively inefficient in that only about 270.degree. of the tape track is actually available for reading or writing by a circular rotor due to deviation of the winding from a circular shape to a helicoidal shape. Consequently, the region of the tape which is worn by the moving head (i.e., 360.degree.) considerably exceeds the portion which can be accessed (270.degree.). Third, the 360.degree. tape wrap device is not readily adaptable to the use of multiple heads. Multiple heads would merely track one another in such a device.
The 180.degree. wrap devices also suffer from significant limitations. While such devices do permit gradual head penetration of the tape, they do so at the expense of a considerable proportion of the potentially usable tape track. The maximum length of each available track is necessarily less than 180.degree. by at least required stabilization zones for entry and exit, and these stabilization zones constitute a relatively large proportion of the short 180.degree. track.
In addition, both conventional devices use relatively cumbersome mounting arrangements. Both mounting arrangements are essentially planar in nature and therefore relatively elongated. Moreover, because they are planar (two-dimensional), they present difficulties in mounting the components with the required high levels of three-dimensional tolerance (typically in the mil or one-tenth mil range).